Linux驱动程序开发入门指南
理解 Linux 驱动程序的基本概念
Linux 驱动程序是内核模块的一部分，负责与硬件设备通信。驱动程序将硬件操作抽象为统一的接口，供用户空间程序调用。内核模块可以动态加载和卸载，无需重新编译内核。
准备开发环境
安装必要的工具链和内核头文件。在基于 Debian 的系统上，运行以下命令：
sudo apt-get install build-essential linux-headers-$(uname -r)
确保系统已配置为允许模块加载和调试。编辑 /etc/sysctl.conf，添加或修改以下行：
kernel.printk = 7 4 1 7
编写最简单的内核模块
创建一个名为 hello.c 的文件，内容如下：
#include <linux/init.h>
#include <linux/module.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
static int __init hello_init(void) {
printk(KERN_INFO "Hello, world!\n");
return 0;
}
static void __exit hello_exit(void) {
printk(KERN_INFO "Goodbye, world!\n");
}
module_init(hello_init);
module_exit(hello_exit);
创建 Makefile：
obj-m := hello.o
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
all:
make -C $(KDIR) M=$(PWD) modules
clean:
make -C $(KDIR) M=$(PWD) clean
编译并加载模块：
make
sudo insmod hello.ko
查看内核日志：
dmesg | tail
卸载模块：
sudo rmmod hello
实现字符设备驱动程序
字符设备驱动程序是最常见的驱动程序类型之一。创建一个名为 chardev.c 的文件：
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#define DEVICE_NAME "chardev"
#define BUF_LEN 80
static int Major;
static char msg[BUF_LEN];
static char *msg_Ptr;
static int device_open(struct inode *inode, struct file *file) {
msg_Ptr = msg;
try_module_get(THIS_MODULE);
return 0;
}
static int device_release(struct inode *inode, struct file *file) {
module_put(THIS_MODULE);
return 0;
}
static ssize_t device_read(struct file *filp, char *buffer, size_t length, loff_t *offset) {
int bytes_read = 0;
if (*msg_Ptr == 0) return 0;
while (length && *msg_Ptr) {
put_user(*(msg_Ptr++), buffer++);
length--;
bytes_read++;
}
return bytes_read;
}
static ssize_t device_write(struct file *filp, const char *buff, size_t len, loff_t *off) {
sprintf(msg, "%s(%zu letters)", buff, len);
msg_Ptr = msg;
return len;
}
static struct file_operations fops = {
.read = device_read,
.write = device_write,
.open = device_open,
.release = device_release
};
static int __init chardev_init(void) {
Major = register_chrdev(0, DEVICE_NAME, &fops);
if (Major < 0) {
printk(KERN_ALERT "Registering char device failed with %d\n", Major);
return Major;
}
printk(KERN_INFO "Registered char device with major number %d\n", Major);
return 0;
}
static void __exit chardev_exit(void) {
unregister_chrdev(Major, DEVICE_NAME);
printk(KERN_INFO "Unregistered char device\n");
}
module_init(chardev_init);
module_exit(chardev_exit);
更新 Makefile：
obj-m := chardev.o
测试驱动程序：
make
sudo insmod chardev.ko
cat /proc/devices | grep chardev
sudo mknod /dev/chardev c 250 0
sudo chmod 666 /dev/chardev
echo "Test message" > /dev/chardev
cat /dev/chardev
处理中断和 DMA
对于需要处理硬件中断的驱动程序，需要注册中断处理程序：
#include <linux/interrupt.h>
irqreturn_t irq_handler(int irq, void *dev_id) {
/* 处理中断 */
return IRQ_HANDLED;
}
/* 在初始化函数中 */
int result = request_irq(irq_number, irq_handler, IRQF_SHARED, "my_device", dev_id);
DMA 操作需要使用内核提供的 DMA API：
#include <linux/dma-mapping.h>
dma_addr_t dma_handle;
void *buffer = dma_alloc_coherent(dev, size, &dma_handle, GFP_KERNEL);
/* 使用缓冲区 */
dma_free_coherent(dev, size, buffer, dma_handle);
调试和测试驱动程序
使用 printk 输出调试信息，可以通过 dmesg 查看。更高级的调试可以使用 kgdb 或 kprobes。
创建测试程序验证驱动程序功能：
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
int main() {
int fd = open("/dev/chardev", O_RDWR);
write(fd, "Test", 4);
char buf[100];
read(fd, buf, 100);
printf("Read: %s\n", buf);
close(fd);
return 0;
}
驱动程序发布和维护
遵循内核编码风格，使用 checkpatch.pl 检查代码：
./scripts/checkpatch.pl -f my_driver.c
考虑将驱动程序提交到主线内核，需要遵循内核社区的贡献指南。维护驱动程序时，注意兼容不同内核版本，处理 API 变化。
安全考虑
验证所有用户空间输入，防止缓冲区溢出。使用内核提供的安全函数如 copy_from_user 和 copy_to_user。实现适当的权限检查，限制设备访问。
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